There are many known welding-type systems used to provide a welding-type output or welding-type power for many known applications. Welding-type system, as used herein, includes any device capable of supplying welding, plasma cutting, and/or induction heating power including inverters, converters, choppers, resonant power supplies, quasi-resonant power supplies, etc., as well as control circuitry and other ancillary circuitry associated therewith. Welding-type output, as used herein, includes outputs suitable for welding, plasma or heating. Welding type power, as used herein, refers to welding, plasma or heating power.
Examples of prior art welding-type systems include those described in Method of Designing and Manufacturing Welding-Type Power Supplies, Albrecht, filed Sep. 19, 2001, application Ser. No. 09/956,401, which issued on Mar. 30, 2004 as U.S. Pat. No. 6,713,721; Pendant Control for a Welding-Type System, L. Thomas Hayes, filed Sep. 19, 2001, application Ser. No. 09/956,502, which issued on Oct. 28, 2003 as U.S. Pat. No. 6,639,182; Welding-Type Power Supply With A State-Based Controller, Holverson et al, filed Sep. 19, 2001, application Ser. No. 09/956,548, which issued on Jun. 8, 2004 as U.S. Pat. No. 6,747,247; Welding-Type System With Network And Multiple Level Messaging Between Components, Davidson et al., filed Sep. 19, 2001, application Ser. No. 09/957,707, which issued on Dec. 30, 2003 as U.S. Pat. No. 6,670,579; Welding-Type Power Supply With Boot Loader, L. Thomas Hayes, filed Sep. 19, 2001, application Ser. No. 09/956,405, which issued on Jan. 7, 2003 as U.S. Pat. No. 6,504,131; Welding-Type System With Robot Calibration, Rappl et al., filed Sep. 19, 2001, application Ser. No. 09/956,501, which issued on Nov. 4, 2003 as U.S. Pat. No. 6,642,482; and U.S. Pat. No. 6,087,626, Hutchison, et al., Jul. 11, 2000, entitled Method and apparatus for welding. Each of these patents is hereby incorporated by reference.
Some such systems are used for short circuit (MIG) welding, a process where the arc alternates between a short and arc state. A wire electrode is mechanically fed into the weldment by a wire feeder in the short circuit transfer welding process. It is consumed into the weldment via a series of alternating short circuit and arc events. This process is generally referred to as short circuit welding, or short circuit transfer welding. Generally, a welding machine used for short circuit welding includes at least a power source, a controller and a wire feeder.
The short circuit transfer welding process is cyclical. One cycle of the process, as described herein, begins with the beginning of a steady state arc, followed by a short circuit condition, and is completed with the beginning of another steady state arc condition. A typical cycle length is 10 msec. The electrode, and a portion of the base metal, are melted during the short circuit transfer welding process by current flowing through the electrode to the weldment. Generally, a portion of the wire material melts during the arc condition, and is transferred during the short condition.
The event of clearing the short, i.e., the transition from a short circuit to an arc, may be the most violent portion of the process and can produce spatter. The explosive nature of this event has been reduced, by lowering the magnitude of the current prior to or at the short clearing, thereby limiting the power density. Some prior art short arc systems sensed the clearing, and then lowered the current magnitude. Better short arc systems, such as Miller RMD®, predict the short clearing, so the current can be lowered prior to the clearing. The RMD® prediction includes monitoring the second derivative of power.
Short circuits can occur unintentionally in pulse welding. In such situations it is desirable to clear the short in a way to avoid spatter. The prior art short clearing for pulse processes typically reduced the current after the voltage reached a specified threshold, indicating the process is back in an arc. However, clearing a short in this method tends to generate spatter.
Accordingly, a welding type system that performs welding and includes a way to predict the short clearing so that the current may be lowered prior to the short clearing is desirable.